This invention relates generally to an ink jet printing device, and more particularly to an ink jet recording device of the ink-on-demand type composed of an ink jet head and an ink container integral therewith and supported on a moveable carriage. There have been known in the prior art ink jet printers of the ink-on-demand type having an integral construction composed of an ink jet head and an ink container. For example, Japanese Laid-Open Patent Publication No. 50-99436 discloses printer heads as shown in FIGS. 1(A) and 1(B) of the accompanying drawings. The arrangement of FIG. 1(A) has a filter 132 disposed in the bottom of an ink container 112 for preventing air bubbles in a body of ink 124 from flowing toward pressurization chambers 113. In the structure of FIG. 1(B), a filter 132 is filled in an ink container 112 for preventing air bubbles from flowing into a flow passage 127. The prior art printer heads as shown in FIGS. 1(A) and 1(B) however allow supersaturated air in the ink to form air bubbles in the filter 132 when the ink is subjected to a temperature rise. Air bubbles which have somehow passed through the filter 132 for any reason tend to be trapped in a portion of the filter 132, the discharge opening 129 or the flow passage 127. In general, the opening 129 and the flow passage 127 have cross sectional areas much greater than the cross sectional area of flow passages 128 communicating with the pressure chambers 113 in the printer head 111. Therefore, it is difficult to force the trapped air bubbles together with the ink out of the opening 129 and the flow passage 127 as the speed of flow of the ink cannot be increased in the opening 129 and flow passage 127. The conventional printer heads are therefore disadvantageous in that air bubbles are likely to be present in the filter 132, the opening 129 or the flow passage 127 at all times, and any such air bubbles which happen to reach the pressure chambers 113 prevent ink from being expelled from the pressure chambers 113.
Another serious problem with the known ink jet recording devices of the ink-on-demand type is that nozzles tend to be clogged with evaporated ink. To solve this problem, the nozzles are normally closed by covers to prevent ink from evaporating from the nozzles. However, experiments conducted by the inventors have revealed that the covers on the nozzles fail to prevent air bubbles from being formed in the head. One reason for such air bubble formation is considered to be the fact that a concave meniscus 102 (FIG. 2) in a nozzle 101 allows air bubbles to be trapped in the nozzle 101 when covered by a cover or lid 103, or the cover 103 as it approaches the nozzle 101 gets wet irregularly with the ink, permitting air bubbles to be trapped in the nozzle 101.
The body of ink in the ink container is kept in contact with air therein through a free interface. This poses another problem in that the ink surface tends to stir when the ink container is moved by a carriage, thus trapping air bubbles in the ink. According to Japanese Laid-Open Utility Model Publication No. 54-86047 and Japanese Utility Model Publication No. 54-8746, horizontal and vertical partitions are employed to prevent the ink surface from being stirred or undulated as illustrated in FIGS. 3 and 4 of the accompanying drawings. The horizontal partitions 151 shown in FIG. 3, however, are disadvantageous in that air bubbles, having entered lower ink chambers or produced due to a temperature change, cannot move upwardly, and small air bubbles tend to be formed which render the printer head incapable of ink ejection. When the ink surface reaches connector holes 153 communicating between the ink chambers 152, the ink surface is more likely to be stirred at the connector holes 153, causing small air bubbles to be created in the ink. If vertical partitions 154 as shown in FIG. 4 are positioned with less spacing to prevent the ink surface from being stirred, then air bubbles once trapped in the ink are interposed between the partitions 154 and fail to go upwardly. Conversely, if the partitions 154 are spaced more widely, small air bubbles are liable to occur at the free ink surface.
What is needed is an ink jet printer designed to prevent air in the ink from interfering with ejection of ink from the jet nozzle.